Cadmium fluoborate electroplating solution



and pleasing appearance.

CADMIUM' FLUOBORATE .ELECIROPLATING' SOLUTION Ralph E. Alexander, Topangm Calif assignmto r North AmericanAviation, Inc.

No Drawing. Application September 14, 1953, Serial No. 380,101 I This invention pertains to an electroplating solution and more particularly to a cadmium fluoborate electroplating solution having included therein.

It has long been the practicein protecting steel oriron parts from corrosion to provide a platingoficadmium an improved addition: agent on the surface thereof. When so plated, these parts Will not rust and will therefore be protected for use in what would normally be corrosive surroundings. It is conventional to electroplate these parts in a cyanide bath which will produce a lustrous plate having a fine-grain However, the .effi electroplating with such a cyanide bath is relatively low, ranging from around 50 percent to a maximumof about 80 percent. This means'that the bath will'not deposit 100 percent cadmium on'the part to be plated, but will also deposit hydrogen in its place. The hydrogen so deposited leads to the principal disadvantage o'f'the cyanide bath type of cadmium plating, which is a causation of hydrogen embrittlement in the plated part. According to one theory, the hydrogen atoms deposited on the surface of the steel part Will enter the molecular structure beneath the surface of the steel. When several atoms have been so introduced into the steel part, the hydrogen atoms may join together to form hydrogen molecules. A hydrogen molecule comprised of two hydrogen atoms will take up considerably more space than did the two individual atoms prior to their joining together in molecular form. As a result, when a hydrogen molecule is produced it is held within the steel part under tremendous pressure due to the force exerted by the hydrogen molecule in displacing its additional volume. This will cause internal stresses within the steel part which will cause it to fail long before its normal design limits are reached. A steel part subjected to hydrogen embrittlement will have lost most of its ductility, will have a low yield strength and will exhibit little reduction of area under stress prior to failure. The ultimate strength of a part having hydrogen embrittlement may be far below its normal value, in many cases being considerably less than half of the usual strength of material.

The use of cadmium fluoborate as a plating solution has been proposed, and it has been found that this solution is very nearly 100 percent eflicient in its cadmium deposition. This means that the problem of hydrogen embrittlement from this source is entirely obviated. It also means that the plating action is considerably faster than with the conventional cyanide bath. However, cadmium plating .from a conventional cadmium fluoborate bath has been commercially unacceptable. This is because the cadmium deposited will have a dull grey appearance and a large grain structure. Also such a solution, without having any addition agent included therewith, will exhibit relatively poor throwing power thus not plating satisfactorily within recesses and inaccessible areas. Furthermore, the cadmium fluoborate solution will cause treeing in the plated cadmium. This is the growth of crystalline structure exteriorly of the part plated, which crystalline growth will be easily broken off thus promoting roughness, loss of metal and other disadvantages. A cadmium fluoborate bath will also permit only relatively low current densities during the plating operation without seriously impairing the adherence of the plated metal.

Addition agents have been proposed for inclusion with cadmium fluoborate solutions, one of the most common of which is licorice. Such agents have improved the throwing power of the cadmium fluoborate solution and ciency oil have largely eliminated the difliculty of treeing. However, ;the grain structure, color .and appearance of the cadmium plating-has been aided little, if at all..-

resultthere has been practically nocommercial use of cadmium fluoborate electroplating prior to the advent of this invention. By the provisions of this. invention an addition agent is included with a cadmium fluoborate solution whichtwill overcomethe difiiculties previously encountered. l r Therefore, it is an object of this invention to provide a commercially usable, highly efiicient cadmium fluoborate plating solution.

Anotherobjectof,.thisinvention is to provide a means for producing cadmium plating of refined grain structure from a cadmium fluoborate plating bath.

An additional object of this invention is to provide cadmium plating .having improved luster and color, with the absence of treeing.

Still another object of this-invention is to provide a ,piating solution permitting a wide range of usable current densities. v

A further object of this invention is to provide a plating solution whereby improved appearance and grain structure are'obtained without hydrogen embrittlement,

and in which the throwing power is satisfactory.

These and other objects will become apparent from the following detailed description.

According to the provisions of this invention an addition agent is provided for a cadmium fluoborate electroplating? .solution which r will greatly improve the characteristics thereon. The'addition agent so selected shouldube. from the groupof organic compounds known as enzymes. It has been found that pepsin and diastase of malt are particularly satisfactory for this purpose. These compounds, which are similar in their characterlstics, are relatively inexpensive compared with the cost of other enzymes.

A typical cadmium fluoborate plating bath will be an aqueous solution including from 25 to 40 ounces of cadmium fluoborate per gallon of water. Additionally the solution should have between 8 and 15 ounces of ammonium fluoborate per gallon of water. A bath of this type will produce a lusterless, dark cadmium deposit of large grain size. If an enzyme addition agent is included with this bath these and other disadvantages are overcome. The enzyme must be added to the cadmium fluoborate bath in the proper amount in order to obtain the desired effects. The optimum value for this quantity falls in the range of from 0.5 to 1.0 gram per liter of plating solution. Thus from 0.5 to 1.0 gram of pepsin, diastase of malt, rennet or other enzyme should be added to each liter of the cadmium fluoborate solution. Actually the addition agent will provide improved results in plating if added in amounts ranging from 0.2 to 5.0 grams per liter of plating solution. Below 0.2 gram per liter there is little benefit from the use of the addition agent. Above 1.0 gram per liter the use of more addition agent, although not harmful, adds little to the results. There fore, for reasons of economy, it is normally desirable to include no more than one gram per liter of addition agent.

The pH value of the plating bath affects the etficiency of the plating operation and consequently should be kept within certain limits. When an enzyme addition agent is used, the solution should be slightly acid having a pH value in the range of from 3.0 to 4.2. The pH value may be raised as desired with ammonia water, or lowered with fluoboric acid so that a value Within this range is obtained. In order to maintain the pH value of the plating bath, boric acid may be added as a bufi'ering agent in the amount of from 1.0 to 6.0 ounces per gallon of solution.

Plating with this solution is then conventional as with any cadmium fluoborate bath. The parts, of course, should be thoroughly cleaned before insertion in the plating bath in order that a continuous plate will be obtained. By virtue of the fact that the cadmium fluoborate bath is nearly percent efficient, plating time will be cut over that required for a cyanide bath. It has additionally been found that a wider range of current densities is possible with the solution having the enzyme addition agent than is the case in a cadmium fluoborate solution -a good luster. fiuoborate solution with this addition agent is more than without this agent, or with another type of addition agent.

"It is possible to use current densities up to around 100 amperes per square foot before there will be produced dark, loosely adherent burned deposits. Of course current densities of any value up to this maximum are a high current density is possible further adds to the speed and flexibilityof use ofthe plating solution of this invention. i

When a. steel or iron part is plated with the solution of this invention, it will have the refined grain structure more nearly approaching the characteristics of native .1

cadmium than that possible with other cadmium fluoborate solutions. The color of the plating is light and has The throwing power of the cadmium adequate and there is no tendency toward treeing. The adherence of the cadmium is also very good. It has been found that parts so plated will exhibit no tendency toward hydrogen embrittlement whereby there is no loss of strength by virtue of the cadmium plating.

It can therefore be seen from the above description that I have provided an improved cadmium fluoborate solution which will obviate the difficulties normally attendant such a plating bath. The use of an enzyme such as pepsin or diastase of malt in the cadmium fiuoborate plating solution will enable the solution to obtain vastly improved results. Plating with such a bath is commercially acceptable in appearance and will protect highly stressed parts without causing any loss of ductility or strength thereof.

The foregoing detailed description is to be clearly understood as given by Way of example only, the spirit and scope of this invention being limited only by the appended claims.

I claim:

l. An electroplating bath comprising an aqueous solution of cadmium fluoborate containing from 0.2 to 5.0 grams per liter of an enzyme selected from the group consisting of pepsin, diastase of malt and rennet.

2. An electroplating bath comprising an aqueous solution of cadmium fluoborate ranging from 25 to ounces per gallon of water, ammonium fluoborate ranging from 8 to 15 ounces per gallon of Water, and containing from 0.2 to 5.0 grams per liter of an enzyme selected from the group consisting of pepsin, rennet and diastase of malt.

3. An electroplating bath as recited in claim 2 in which the pH, value of said solution is in the range of from'3.0'to 4.2.

4. A cadmium fluoborate aqueous electroplating solution containing any enzyme from the group consisting of pepsin, diastase'of malt and rennet in an amount exceeding approximately 0.2 gram per liter of solution and -less than approximately 5.0 grams per liter of solution.

5. An electroplating bath comprising an aqueous solution of from 25 to 40 ounces of cadmium fiuoborate per gallon of water, from 8 to 15 ounces of ammonium fiuoborate per gallon of'water, and containing pepsin ranging in amount from about 0.5 to 1.0 gram per liter of said solution.

6. An electroplating bath comprising an aqueous solution of from 25 to 40 ounces of cadmium fiuoborate per gallon of water, from 8 to 15 ounces of ammonium fluoborate per gallon of water, and containing diastase of malt ranging in amount from about 0.5 to 1.0 gram per liter of said solution.

References Cited in the file of this patent FOREIGN PATENTS 892,991 Germany Oct. 12, 1953 

1. AN ELECTROPLATING BATH COMPRISING AN AQUEOUS SOLUTION OF CADMIUM FLUOBORATE CONTAINING FROM 0.2 TO 5.0 GRAMS PER LITER OF AN ENZYME SELECTED FROM THE GROUP CONSISTING OF PERPSIN, DIASTASE OF MALT AND RENNET. 